AU IRS LSD 3.45 to 4.1

Sprint347 · 21-12-2015, 04:32 PM

Hi All

I've done plenty of searching but with limited success.

Has anyone here installed 4.1 gears into an AU IRS LSD?

I'm guessing M78 Dana Spicer gears are suitable for this application?

Is there a speedo cog available for this ratio to suit BTR 4 speed?

Thanks in advance.

S

ebgtjames · 21-12-2015, 04:57 PM

Jarad has 4.11s...

http://www.fordforums.com.au/showthr...1253752&page=7

T MAN · 21-12-2015, 05:11 PM

i have not done 4.11 but i have 3.91..
4.11 are available, but just like the 3.91 the 4.11 are actually m75 dana gears, dana spicer only make them in m75 series.
all this means is the pinion needs to be shimmed for fitment in our m78 housings.

and unfortunatly there is no speedo gear big enough for 3.9 or 411 gears. the largest made was a 23 tooth which is ment for 3.45 ration with 16" low profile tyres.. this can be used on larger rims for 3.77 ratio but its still around kmh out...
so a speedo corrector would be the easiest way to get around it...

NCII40 · 21-12-2015, 06:47 PM

Hey Mate

I would highly recommend a guy who built my Diff, His name is Glenn (GJV Automotive) 0431557226
He did an excellent job on my 389 LSD upgrade and he knows BW Diffs..
He has a ebay store too, His username is Vicmelboz thats i how i found him
He does 4.11 to and knows how to modify them to fit

Sox · 21-12-2015, 08:50 PM

Quote:

Originally Posted by T MAN

i have not done 4.11 but i have 3.91..
4.11 are available, but just like the 3.91 the 4.11 are actually m75 dana gears, dana spicer only make them in m75 series.
all this means is the pinion needs to be shimmed for fitment in our m78 housings.

and unfortunatly there is no speedo gear big enough for 3.9 or 411 gears. the largest made was a 23 tooth which is ment for 3.45 ration with 16" low profile tyres.. this can be used on larger rims for 3.77 ratio but its still around kmh out...
so a speedo corrector would be the easiest way to get around it...

Should be able to fit an internal 7 tooth gear to sort the speedo.

T MAN · 21-12-2015, 08:53 PM

Quote:

Originally Posted by Sox

Should be able to fit an internal 7 tooth gear to sort the speedo.

Hmm. Never thought of trying that.. is there a 7 tooth available for the btr?...

Sox · 21-12-2015, 08:58 PM

Quote:

Originally Posted by T MAN

Hmm. Never thought of trying that.. is there a 7 tooth available for the btr?...

As far as I'm aware there is.

mcfly94 · 21-12-2015, 11:20 PM

Im on dana 3.9's and a precision helical lsd.
As TMAN said there a 75 series set shimmed to suit our 78 series diffs.

I couldnt find a gear for life of me searched high and low, american forums, australian forums. Gave up installed a speedo corrector, drove around for like 3 months got sick of bashing the limiter on WOT and installed a QH and made some adjustments.

Now all good!

Id upgrade your diff centre while your at it!

Sprint347 · 22-12-2015, 09:21 AM

Thanks everyone for the replies.

I saw Dana spicer gears advertised as m75, m76 and m78 which was confusing. I've since discovered they're effectively the same (m75 has slightly smaller outside diameter and m76 is IRS) but they're interchangeable.

I do have a Quarterhorse, I didn't realise that can do speedo calibration too.

Hopefully I'll get secure some gears today and get the ball rolling - first gear in BTR autos is terrible.

mcfly94 · 22-12-2015, 12:57 PM

QH can calibrate Trans only speedo corrector still required. Placement of one however can eliminate the need to make adjustments in the trans

Sprint347 · 22-12-2015, 04:25 PM

Awesome cheers, just reading into the Jaycar speedo corrector devices now.

I've purchased a set of 4.1 spicer gears - can't wait!

mcfly94 · 22-12-2015, 05:45 PM

Yeah don't bother with them I got rid of mine. Wouldnt pick up au signal as they changed the model. Unless you can get hold of the older model.
My auto electrician end up using there own was $120 in comparison to the jaycar $40 and much larger, dunno what brand it I'd but it works!

347 mont · 14-01-2016, 03:00 AM

Quote:

Originally Posted by mcfly94

Yeah don't bother with them I got rid of mine. Wouldnt pick up au signal as they changed the model. Unless you can get hold of the older model.
My auto electrician end up using there own was $120 in comparison to the jaycar $40 and much larger, dunno what brand it I'd but it works!

Aaaahhh that's why we couldn't get the Jaycar corrector to work on my AU11, ended up taking

it to an auto electrician to fit and still had no success. Interesting.

NCII40 · 02-07-2017, 11:41 AM

Solved

https://www.fordforums.com.au/showthread.php?t=11464112

Bossxr8 · 02-07-2017, 07:37 PM

A place like gauge works who calibrate speedos should be able to sort it out even if factory gears aren't useable. They got my speedo spot on after i went 3.9's.

Climaxxx · 25-02-2019, 04:08 PM

Quote:

Originally Posted by Bossxr8

A place like gauge works who calibrate speedos should be able to sort it out even if factory gears aren't useable. They got my speedo spot on after i went 3.9's.

Did you notice a big difference in gears? Was thinking of changing to 3.73. What do you need to make the speedo work properly?

Bossxr8 · 26-02-2019, 10:30 AM

Quote:

Originally Posted by Climaxxx

Did you notice a big difference in gears? Was thinking of changing to 3.73. What do you need to make the speedo work properly?

It felt stronger with the 3.9's. Economy around town improved as well. Didn't notice any real difference to highway economy either.

It will just need a change in speedo gear to get the speedo right.